截面积乘以速度的物理量

Q: 請問是什麼物理量?

A physical quantity (物理量) is a physical property that can be quantified. This means it can be measured and/or calculated and expressed in numbers. The value of a physical quantity is expressed as the product of a numerical value and a physical unit.

Examples of physical quantities are: mass, density, volume, temperature, velocity, displacement, current, voltage, resistance, pressure, energy, momentum ...... etc.

Q: 它有跟密度有關嗎?

Density itself is a physical quantity, as it is a property of matter that can be measured (i.e. quantified) and expressed in specific units, kg/m^3 or grams/cm^2

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Q:截面积乘以速度的物理量

The unit for the product of cross-sectional area and velocity can be dervied.

unit for cross-sectional area = m^2
unit for velocity = m/s
Thus, unit for [cross-sectional area] x [velocity] = m^2 x m/s = m^3/s

Clearly, the unit indicates a physical quantity of 'volume per unit time'. This is, in fact, gives the volume of fluid passing through a given sectional area in a unit time interval (i.e. in 1 second).